In convention in order to delivery a pizza which has been cooked by a cooker such as an oven to an aimed site while maintaining the hot state, it has been known to utilize a container made of a material having good heat reserving properties (Japanese Patent Laid-Open No. 8-150081).
In addition, techniques have also been known for delivering a food with its hot state in which a heat-reserving box having a battery and a heater is used (Japanese Patent Laid-Open No. 7-241246 and Japanese Utility Model Laid-Open No. 4-124972).
Further, a device has been made in which a chemical heating element is used instead of the battery and heater (Japanese Utility Model Laid-Open No. 61-74564).
However, these techniques are disadvantageous in that even if any material having very good heat reserving properties is used to produce a container for pizza, there is a limitation for the heat reserving properties, for example, in such a case where the site to be delivered is very far or in such a case where it takes much times due to heavy traffic, resulting in the pizza getting cold.
It should be absolutely avoided to deliver a pizza at breakneck speed for the purpose of preventing the pizza form getting cold, in terms of falling into the dangerous situation of the life.
An attempt has been made for solving the problem to utilize a heat-reserving device having a battery and a heater, leading to solution of the problem to some extents. However, the device, which has a complicated construction, leads to new disadvantages such as expensive cost and heavy weight.
As for the use of a chemical heating element for the purpose of heat reservation, there is a problem that the chemical heating element can not be used again.